Wiley

2‐Acetyl‐1‐pyrroline (2AP), the volatile compound that provides the ‘popcorn‐like’ aroma in a large variety of cereal and food products, is widely found in nature. Deficiency in amino aldehyde dehydrogenase (AMADH) was previously shown to be the likely cause of 2AP biosynthesis in rice (Oryza sativa L.). In this study, the validity of this mechanism was investigated in soybeans (Glycine max L.). An assay of AMADH activity in soybeans revealed that the aromatic soybean, which contains 2AP, also lacked AMADH enzyme activity. Two genes, GmAMADH1 and GmAMADH2, which are homologous to the rice Os2AP gene that encodes AMADH, were characterized. The transcription level of GmAMADH2 was lower in aromatic varieties than in nonaromatic varieties, whereas the expression of GmAMADH1 did not differ. A double nucleotide (TT) deletion was found in exon 10 of GmAMADH2 in all aromatic varieties. This variation caused a frame‐shift mutation and a premature stop codon. Suppression of GmAMADH2 by introduction of a GmAMADH2‐RNAi construct into the calli of the two nonaromatic wild‐type varieties inhibited the synthesis of AMADH and induced the biosynthesis of 2AP. These results suggest that deficiency in the GmAMADH2 product, AMADH, plays a similar role in soybean as in rice, which is to promote 2AP biosynthesis. This phenomenon might be a conserved mechanism among plant species.

Plants inevitably encounter environmental adversities, including abiotic and biotic stresses, which significantly impede plant growth and reduce crop yield. Thus, fine‐tuning the fate and function of stress‐responsive RNAs is indispensable for plant survival under such adverse conditions. Recently, post‐transcriptional RNA modifications have been studied as a potent route to regulate plant gene expression under stress. Among over 160 mRNA modifications identified to date, N⁶‐methyladenosine (m⁶A) in mRNAs is notable because of its multifaceted roles in plant development and stress response. Recent transcriptome‐wide mapping has revealed the distribution and patterns of m⁶A in diverse stress‐responsive mRNAs in plants, building a foundation for elucidating the molecular link between m⁶A and stress response. Moreover, the identification and characterization of m⁶A writers, readers and erasers in Arabidopsis and other model crops have offered insights into the biological roles of m⁶A in plant abiotic stress responses. Here, we review the recent progress of research on mRNA modifications, particularly m⁶A, and their dynamics, distribution, regulation and biological functions in plant stress responses. Further, we posit potential strategies for breeding stress‐tolerant crops by engineering mRNA modifications and propose the future direction of research on RNA modifications to gain a much deeper understanding of plant stress biology.

Plants have evolved numerous constitutive and inducible defence mechanisms to cope with biotic and abiotic stresses. These stresses induce the expression of various genes to activate defence‐related pathways that result in the release of defence chemicals. One of these defence mechanisms is the oxylipin pathway, which produces jasmonates, divinylethers and green leaf volatiles (GLVs) through the peroxidation of polyunsaturated fatty acids (PUFAs).GLVs have recently emerged as key players in plant defence, plant–plant interactions and plant–insect interactions. SomeGLVs inhibit the growth and propagation of plant pathogens, including bacteria, viruses and fungi. In certain cases,GLVs released from plants under herbivore attack can serve as aerial messengers to neighbouring plants and to attract parasitic or parasitoid enemies of the herbivores. The plants that perceive these volatile signals are primed and can then adapt in preparation for the upcoming challenges. Due to their ‘green note’ odour,GLVs impart aromas and flavours to many natural foods, such as vegetables and fruits, and therefore, they can be exploited in industrial biotechnology. The aim of this study was to review the progress and recent developments in research on the oxylipin pathway, with a specific focus on the biosynthesis and biological functions ofGLVs and their applications in industrial biotechnology.

Bacillus thuringiensis (Bt) là một loại vi khuẩn trong đất hình thành bào tử trong giai đoạn trì trệ của chu trình phát triển của nó. Các bào tử chứa các tinh thể, chủ yếu là một hoặc nhiều protein Cry và/hoặc Cyt (còn được gọi là δ-endotoxin) có hoạt tính diệt côn trùng mạnh và đặc hiệu. Các chủng Bt khác nhau tạo ra các loại độc tố khác nhau, mỗi loại ảnh hưởng đến một nhóm phân loại côn trùng hẹp. Do đó, độc tố Bt đã được sử dụng như thuốc trừ sâu dạng phun bề mặt để bảo vệ cây trồng, và gần đây hơn, các protein đã được biểu hiện trong cây trồng chuyển gen để tạo ra khả năng kháng sâu bệnh tự nhiên. Cây trồng chuyển gen Bt đã đạt được thành công áp đảo và mang lại lợi ích, dẫn đến sản lượng thu hoạch cao hơn và giảm việc sử dụng thuốc trừ sâu hóa học và nhiên liệu hóa thạch. Tuy nhiên, việc triển khai chúng đã thu hút một số chỉ trích, đặc biệt liên quan đến khả năng tiến hóa của các chủng côn trùng kháng thuốc. Ở đây, chúng tôi xem xét tiến bộ gần đây trong phát triển công nghệ Bt và các biện pháp đối phó đã được giới thiệu để ngăn ngừa sự phát triển của quần thể côn trùng kháng thuốc.

Genetic modification of plant cell walls has been posed to reduce lignocellulose recalcitrance for enhancing biomass saccharification. Since cellulose synthase (CESA) gene was first identified, several dozen CESA mutants have been reported, but almost all mutants exhibit the defective phenotypes in plant growth and development. In this study, the rice (Oryza sativa) Osfc16 mutant with substitutions (W481C, P482S) at P‐CR conserved site in CESA9 shows a slightly affected plant growth and higher biomass yield by 25%–41% compared with wild type (Nipponbare, a japonica variety). Chemical and ultrastructural analyses indicate that Osfc16 has a significantly reduced cellulose crystallinity (CrI) and thinner secondary cell walls compared with wild type. CESA co‐IP detection, together with implementations of a proteasome inhibitor (MG132) and two distinct cellulose inhibitors (Calcofluor, CGA), shows that CESA9 mutation could affect integrity of CESA4/7/9 complexes, which may lead to rapid CESA proteasome degradation for low‐DP cellulose biosynthesis. These may reduce cellulose CrI, which improves plant lodging resistance, a major and integrated agronomic trait on plant growth and grain production, and enhances biomass enzymatic saccharification by up to 2.3‐fold and ethanol productivity by 34%–42%. This study has for the first time reported a direct modification for the low‐DP cellulose production that has broad applications in biomass industries.

Polyhydroxyalkanoate bio‐based plastics made from renewable resources can reduce petroleum consumption and decrease plastic waste disposal issues as they are inherently biodegradable in soil, compost and marine environments. In this paper, the successful engineering of the biomass crop switchgrass (Panicum virgatum L.) for the synthesis of polyhydroxybutyrate (PHB) is reported. Polymer production was monitored in more than 400 primary transformants grown under in vitro and glasshouse conditions. Plants containing up to 3.72% dry weight of PHB in leaf tissues and 1.23% dry weight of PHB in whole tillers were obtained. Results from the analysis of the polymer distribution at the cellular and whole plant levels are presented, and target areas for the improvement of PHB production are highlighted. Polymer accumulation was also analysed in the T₁ generation obtained from controlled crosses of transgenic plants. This study presents the first successful expression of a functional multigene pathway in switchgrass, and demonstrates that this high‐yielding biomass crop is amenable to the complex metabolic engineering strategies necessary to produce high‐value biomaterials with lignocellulose‐derived biofuels.

A wheat cDNA microarray consisting of 5739 expressed sequence tags (ESTs) was used to investigate the transcriptome patterns of the glume, lemma, palea, anther, ovary and rachis dissected from infected wheat spikes after inoculation with the fungus Fusarium graminearum, the causal agent of fusarium head blight (FHB) disease. Stringent conditions were employed to reduce the false discovery rate. The significance analysis of microarrays (SAM) was used to identify transcripts that showed a differential response between fungal‐challenged vs. control plants. To verify the microarray data, Northern blot analysis was carried out on randomly selected up‐regulated clones. We observed 185 (3.2%) up‐regulated and 16 (0.28%) down‐regulated ESTs in the six organs constituting the wheat spike. Many up‐regulated ESTs (46.67%) showed no homology with sequences of known functions, whereas others showed homology with genes involved in defence and stress responses, the oxidative burst of H₂O₂, regulatory functions, protein synthesis and the phenylpropanoid pathway. The monitoring of genes in specific organs avoided the averaging of expression values over multiple organs that occurs when using data from the whole spike. Our data allowed us to uncover new up‐regulated genes expressed in specific organs. The study revealed that each organ had a defined and distinctive transcriptome pattern in response to F. graminearum infection.

An expression Quantitative Trait Locus or eQTL is a chromosomal region that accounts for a proportion of the variation in abundance of a mRNA transcript observed between individuals in a genetic mapping population. A single gene can have one or multiple eQTLs. Large scale mRNA profiling technologies advanced genome‐wide eQTL mapping in a diverse range of organisms allowing thousands of eQTLs to be detected in a single experiment. When combined with classical or trait QTLs, correlation analyses can directly suggest candidates for genes underlying these traits. Furthermore, eQTL mapping data enables genetic regulatory networks to be modelled and potentially provide a better understanding of the underlying phenotypic variation. The mRNA profiling data sets can also be used to infer the chromosomal positions of thousands of genes, an outcome that is particularly valuable for species with unsequenced genomes where the chromosomal location of the majority of genes remains unknown. In this review we focus on eQTL studies in plants, addressing conceptual and technical aspects that include experimental design, genetic polymorphism prediction and candidate gene identification.

The green alga Chlamydomonas reinhardtii does not synthesize high‐value ketocarotenoids like canthaxanthin and astaxanthin; however, a β‐carotene ketolase (CrBKT) can be found in its genome. CrBKT is poorly expressed, contains a long C‐terminal extension not found in homologues and likely represents a pseudogene in this alga. Here, we used synthetic redesign of this gene to enable its constitutive overexpression from the nuclear genome of C. reinhardtii. Overexpression of the optimized CrBKT extended native carotenoid biosynthesis to generate ketocarotenoids in the algal host causing noticeable changes the green algal colour to reddish‐brown. We found that up to 50% of native carotenoids could be converted into astaxanthin and more than 70% into other ketocarotenoids by robust CrBKT overexpression. Modification of the carotenoid metabolism did not impair growth or biomass productivity of C. reinhardtii, even at high light intensities. Under different growth conditions, the best performing CrBKT overexpression strain was found to reach ketocarotenoid productivities up to 4.3 mg/L/day. Astaxanthin productivity in engineered C. reinhardtii shown here might be competitive with that reported for Haematococcus lacustris (formerly pluvialis) which is currently the main organism cultivated for industrial astaxanthin production. In addition, the extractability and bio‐accessibility of these pigments were much higher in cell wall‐deficient C. reinhardtii than the resting cysts of H. lacustris. Engineered C. reinhardtii strains could thus be a promising alternative to natural astaxanthin producing algal strains and may open the possibility of other tailor‐made pigments from this host.